1. Field
Implementations of the invention relate to autonomic data caching and copying on a Storage Area Network (SAN) aware file system using copy services.
2. Description of the Related Art
Computing systems often include one or more host computers (“hosts”) for processing data and running application programs, direct access storage devices (DASDs) for storing data, and a storage controller for controlling the transfer of data between the hosts and the DASD. Storage controllers, also referred to as control units or storage directors, manage access to a storage space comprised of numerous hard disk drives, otherwise referred to as a Direct Access Storage Device (DASD). Hosts may communicate Input/Output (I/O) requests to the storage space through the storage controller.
Storage controllers may provide copy services. With the copy services, data on one storage device, such as a DASD, may be copied to the same or another storage device so that access to data volumes can be provided from two different devices or to have a backup copy.
International Business Machines Corporation (IBM), the assignee of the subject patent application, provides remote copy services for maintaining remote copies of data at a secondary storage device, including extended remote copy (XRC) and peer-to-peer remote copy (PPRC). These systems provide techniques for recovering data updates between a last, safe backup and a system failure. Such data shadowing systems can also provide an additional remote copy for non-recovery purposes, such as local access at a remote site.
Another example of a copy service is a point-in-time copy, which involves physically copying all the data from source volumes to target volumes so that the target volume has a copy of the data as of a point-in-time. A point-in-time copy can also be made by logically making a copy of the data and then only copying data over when necessary, in effect deferring the physical copying, and this is referred to as an “instant virtual copy” operation or “fast replicate function.”
Instant virtual copy operations work by modifying metadata such as relationship tables or pointers to treat a source data object as both the original and copy. In response to a host's copy request, the storage subsystem immediately reports creation of the copy without having made any physical copy of the data. Only a “virtual” copy has been created, and the absence of an additional physical copy is completely unknown to the host. The host or storage subsystem may even proceed to create an actual, physical copy of the original data object during background processing, or at another time.
One such instant virtual copy operation is known as a FlashCopy® operation. Further details of the FlashCopy® operations are described in the commonly assigned U.S. Pat. No. 6,661,901, issued on Aug. 26, 2003, entitled “Method, System, and Program for Maintaining Electronic Data as of a Point-in-Time”, which patent application is incorporated herein by reference in its entirety.
Some conventional systems provide a global file system. That is, server computers may be connected by a network to storage controllers storing files. A file system may include files across the server computers. A file system may be described as a system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure. Thus, a file system includes files along with the ability to access (e.g., store, retrieve, modify, and delete) the files. File access times and speeds with a global file system across long distances may be slow due to the distance that data must travel for a file access. That is, when a request for data is sent to a server computer that is far from the computer generating the request, it may take some time to access the file and return the requested data.
Some conventional systems cache data locally, by geography, using replicated server computers. In particular, a number of server computers are connected together over a large geographic region (e.g., across different states within the United States), and data is replicated at each of the servers. Then, requests for data may be routed to the server computer geographically closest to the computer from which the request was generated. However, it is often difficult to maintain the copies of the data in synch.
Therefore, there is a continued need in the art for improved file access.